Most electronic devices such as servers, computers and the like, are made up of various electronic components within some sort of metal box or chassis. In particular, many servers now fit on individual circuit boards known as “blades” and are placed within a chassis conforming to the PCI Industrial Computer Manufacturers Group (PICMG) Advanced Telecom Computing Architecture (ATCA) 3.0 standard, published January 2003. The ATCA standard defines an open switch fabric-based platform delivering an industry standard high performance, fault tolerant, and scalable solution for next generation telecommunications and data center equipment. The development of the ATCA standard is being defined by the PCI Industrial Computer Manufacturers Group (PICMG)—the same group that created the highly successful Compact PCI standard. The ATCA 3.0 base specification defines the physical and electrical characteristics of an off-the-shelf, modular chassis based on switch fabric connections between hot-swappable blades. Specifically, the ATCA 3.0 base specification defines the frame (rack) and shelf (chassis) form factors, core backplane fabric connectivity, power, cooling, management interfaces, and the electromechanical specification of the ATCA-compliant boards. The ATCA 3.0 base specification also defines a power budget of 200 Watts (W) per board, enabling high performance servers with multi-processor architectures and multi gigabytes of on-board memory.
During operation, each server's components emit electromagnetic radiation and also generate heat. To avoid electromagnetic interference or successibility from other systems with nearby components or devices, it is desirable to prevent the electromagnetic radiation from leaving or entering the chassis. For optimum radiation protection, the chassis should be a completely closed metal box, which would block all the electromagnetic radiation from entering or leaving the box. For optimum heat removal, however, there would either be no chassis at all or the chassis would be a box with highly porous sides to allow substantial airflow and therefore substantial cooling of the components.
The requirements for electromagnetic radiation and heat transfer therefore conflict: the optimum radiation solution would prevent heat removal from the chassis, while the optimum heat solution would not provide adequate radiation suppression. In existing applications, a compromise solution has been to make the chassis a substantially solid box with electromagnetic interference (EMI) filters covering air outlets on one or more sides of the chassis. EMI filters allow air to flow through them while preventing passage of electromagnetic radiation.
As applications have become more demanding their power usage, and therefore the heat they generate, has increased substantially, meaning that more, bigger and/or faster fans are needed to draw cool air into the chassis and expel hot air from the chassis through the EMI filter. More or bigger fans, however, generate substantially more noise, both mechanical noise from the fan mechanisms themselves and noise from the airflow they create. In some cases, the noise is so substantial that it exceeds safety guidelines. Existing EMI filters have been adequate for limiting or reducing EMI emissions from the chassis while allowing adequate heat transfer, but these filters do nothing to reduce or eliminate noise emanating from the interior of the chassis. Attempts to reduce the noise output have focused on modifying the mechanisms and aerodynamics of the fans.